Image forming devices that detachably accommodate a plurality of process cartridges are well-known in the art.
One of such printers includes a main body and an image forming unit detachably mountable in the main body. The image forming unit supports a plurality of process cartridges (for example, see Japanese Patent Application Publication No. 2010-008472).
In this printer, the image forming unit includes a waste toner box to store waste toner, and the main body includes a belt waste-toner conveying tube. The belt waste-toner conveying tube is configured to convey waste toner collected by a belt cleaning device to the waste toner box.